The invention relates to the grinding of the flanks of gear teeth, more particularly, but not exclusively, on cylindrical gearwheels, by means of at least one grinding wheel, in which feed motions between the workpiece and the grinding wheel are superimposed upon a normal generating motion between the workpiece and the grinding wheel and in a direction transverse to the surface or flank of a tooth being ground in order to vary the theoretical involute form of the tooth flanks in zones radially along the tooth profile and/or axially along the tooth length.
It is common practice to utilise for gear-tooth grinding the so-called zero-degrees method in which two grinding wheels basically include an angle of 0.degree., that is to say they are disposed more or less parallel to each other. In therory there is point contact between the grinding wheel and the workpiece but in order to accentuate somewhat such point contact it is also possible for the grinding wheel axes to be inclined relative to each other by a few degrees. To this end it is important that the contact occurs at the external edge of the grinding wheel and the generating motion between the grinding wheel and the workpiece is related to the base circle of the gear being ground, the two theoretically active grinding points being disposed on a tangent to the base circle.
Using this basic generating method, axial motion of the grinding wheel or wheels can be controlled, for example, by a known arrangement of profile and longitudinal correcting template which act on a double lever system (U.S. Pat. No. 3,044,221). Such axial movements of the grinding wheel give profile correction (generally in the form of a tooth tip and/or tooth root reduction) of the tooth uniformly over the entire length of the tooth. The aforementioned specification also describes how the profile can be modified at different axial zones to give a reduction of thickness at the ends of the teeth. An oval contact pattern therefore obtains in contact with the tooth flanks of a mating wheel when such gearwheels are paired.
The previously known methods for modifying gear tooth flank profiles can be inadequate in certain instances, as for example in gear wheels for power transmissions that operate under maximum loadings with extreme tooth pressures and/or circumferential velocities, and also in rolling wheels, that is to say gear tools for the finish rolling of gearwheels. Such applications may require helix corrections or other tooth flank corrections in which the tooth profile varies continuously along the tooth width.